(1) FIELD OF THE INVENTION
This invention relates to a method for processing of imagewise exposed color photographic light-sensitive elements containing silver halide (hereinafter, referred to as "color photographic elements") and more particularly, to an improved photographic process which enables sufficient de-silvering in a shortened time and produces good quality color reproductions.
(2) DESCRIPTION OF THE PRIOR ART
Basic processes for processing color photographic elements generally include a color development step and desilvering step. In the color development, imagewise exposed silver halide is reduced by a color developing agent to form metallic silver and the oxidized color developing agent reacts with a coupler (or dye forming agent) to form a color image. In the subsequent de-silvering step, the metallic silver formed in the color development is oxidized by an oxidizing agent (generally called "a bleaching agent") and the oxidized silver is then dissolved by a silver ion complexing agent generally called a fixing agent. This de-silvering step essentially leaves a dye image on the color photographic elements.
The de-silvering step is done with either a bleaching bath containing a bleaching agent followed by a fixing bath containing a fixing agent or a single bleach-fixing bath (or blixing bath) containing both bleaching and fixing agents.
In addition to these basic steps, the actual procedures of color development processes include various additional steps such as a hardening step, a stopping step, a stabilizing step and a washing step, so as to obtain a dye image having a better photographic and physical quality and a longer stability of the dye image.
Ferricyanides, dichromates, ferric chloride, aminopolycarboxylic acid ferric ion complex salts and persulfates are generally known as the bleaching agent.
However, ferricyanides and dichromates are liable to cause environmental pollution and the use thereof requires special equipment for the treatment of such chemicals. Ferric chloride has various problems in practical use. For example, it forms ferric hydroxide and produces stains in a subsequent washing step. Persulfates have disadvantages in that they are very weak in bleaching power and therefore require an extremely long time for bleaching. In this connection, there has been proposed a method for improving the bleaching power of persulfates by using them together with a bleach accelerator. However, this method is not practical because the use and storage of persulfates are controlled by Fire Prevention Law and consequently require special facilities.
Aminopolycarboxylic acid ferric ion complex salts (or ferric salts of an aminopolycarboxylic acid), particularly ethylenediaminetetraacetic acid ferric ion complex salts (or ferric salts of ethylenediaminetetraaacetic acid) are the bleaching agents most widely used at present because, unlike persulfates, they have few problems regarding environmental pollution and storage. However, the bleaching power of the aminopolycarboxylic acid ferric ion complex salts is not always sufficient. The complex salts may attain the desired de-silvering when they are used to bleach or bleach-fix a low-speed silver halide color photographic element mainly containing silver chlorobromide emulsion, while the complex salts cannot achieve sufficient de-silvering or they need a long time for bleaching when they are used to process a high-speed color photographic element mainly containing silver bromoiodide or silver bromochloroiodide emulsion and having been spectrally-sensitized, especially a color reversal photographic material or a color negative photographic material containing an emulsion of high silver content.
For example, the bleaching time of the photographic color negative light-sensitive material in the bleach bath of the aminopolycarboxylic acid ferric ion complex salt is at least four minutes and it is necessary to take troublesome precautions such as pH control or aeration in order to maintain the bleaching power at the desired level. Even if such precautions are taken, it is not rare that de-silvering is not carried out sufficiently.
For the purpose of complete de-silvering, it is further necessary to treat the element in fixing bath for at least three minutes following the bleaching bath. Accordingly, there is a strong need to shorten the time for de-silvering.
For accelerating the de-silvering, there is known a bleach-fixing solution, as disclosed in German Pat. No. 866,605, which contains both aminopolycarboxylic acid ferric ion complex salt and thiosulfate. However, the bleaching power of this solution is very weak because the blixing solution contains aminopolycarboxylic acid ferric ion complex salt which is weak in oxidizing power (or bleaching power) and thiosulfate which has a reducing power. It is, therefore, very difficult for this blixing solution to attain the desilvering of a photographic color light-sensitive material of high speed and high silver content and consequently, this blixing solution cannot be employed for practical use. Many attempts have been made to overcome these disadvantages of the blixing solution. Examples of such attempts include the addition of iodides or bromides thereto as disclosed in British Patent No. 926, 569 or Japanese Patent Publication No. 11,854/1978 (U.S. Pat. No. 4,040,837) and the incorporation of a high concentration of aminopolycarboxylic acid ferric ion complex salt thereto using triethanolamine as disclosed in Japanese Patent Public Disclosure No. 95,834/1973. However, none of these methods has sufficient effect for practical use.
In addition to its poor de-silvering ability, the blixing solution has another serious drawback in that it reduces the cyan dye formed by color development to the leuco dye and consequently, interferes with color reproduction. It is known that this drawback can be reduced by elevating the pH value of the blixing solution as disclosed in U.S. Pat. No. 3,773,510. This method is, however, almost useless from a practical point of view because the elevation of the pH value results in the weakening of the bleaching power of the solution. U.S. Pat. No. 3,189,452 discloses a method wherein, after blixing, the leuco dye is oxidized to the cyan dye by a ferricyanide bleaching solution. But the use of the ferricyanide brings about the problem of environmental pollution and the bleaching after the blixing has almost no effect on the decrease in the remaining silver ciontent.
As an alternative method for increasing the bleaching power of the aminopolycarboxylic acid ferric ion complex salt, there has been proposed a method wherein various bleaching accelerators are added to the bleaching bath, the blixing bath or the preceding bath.
Examples of such accelerators include various mercapto compounds as disclosed in U.S. Pat. No. 3,893,858, British Pat. No. 138,842 and Japanese Patent Public Disclosure No. 141,623/1978; compounds having disulfide linkage as disclosed in Japanese Patent Public Disclosure No. 95,630/1978 (U.S. Pat. No. 4,169,733); thiazolidine derivatives as disclosed in Japanese Patent Publication No. 9,854/1978; isothiourea derivatives as disclosed in Japanese Patent Public Disclosure No. 94,927/1978 (U.S. Pat. No. 4,144,068); thiourea derivatives as disclosed in Japanese Patent Publication Nos. 8506/1970 (U.S. Pat. No. 3,617,283) and 26,586/1974 (U.S. Pat. No. 3,809,563); thioamide compounds as disclosed in Japanese Patent Public Disclosure No. 42,349/1974 (GB No. 1,394,357); and, dithiocarbamic acid salts as disclosed in Japanese Patent Public Disclosure No. 26,506/1980.
Although some of these accelerators do in fact have a bleach accelerating effect, the effect is, however, not sufficient to meet the need for shortening of the processing time.